Aircraft and other vehicles often use actuators to move various vehicle elements. For example, FIG. 1 is a partially schematic illustration of an aircraft wing 151 and an aileron 152 in accordance with the prior art. In FIG. 1, a first actuator 110 and a second actuator 120 are coupled between the wing 151 and the aileron 152 to move the aileron 152 relative to the wing 151. The first and second actuators 110, 120 are coupled between the wing 151 and the aileron 152 in a parallel configuration. In the parallel configuration, the first and second actuators 110, 120 are each coupled independently between the wing 151 and aileron 152. The parallel configuration is often used to provide an increase in the available force to move the aileron 152. For example, the parallel configuration is often used to provide the required force to deflect a control surface on an aircraft against high aerodynamic forces resulting from high-speed flight.
Additionally, the use of two actuators 110, 120 can provide redundancy in case one of the actuators fails. For example, the actuators 110, 120 often have a bypass mode that allows a failed actuator to move freely when the operative actuator applies a force to move the aileron 152. However, if the failed actuator fails in a manner such that it resists movement (e.g., becomes jammed), the operative actuator must apply a force to overcome any resistance presented by the failed actuator in order to move the aileron 152.
Actuators can also be coupled in series between vehicle elements. Typically, actuators are coupled in series between elements to perform different functions or to provide a larger range of motion than can be obtained with a single actuator. For example, some model aircraft have a low rate actuator and a high rate actuator connected in series between the model aircraft fuselage and the model aircraft elevator. The low rate actuator is used to position the elevator to provide pitch trim and the high rate actuator is used to position the elevator to provide dynamic pitch control.